Negative pressure booster equipment

Abstract

In the negative pressure booster equipment 1 according to the present invention, a groove 27 is provided on the inner peripheral beads 14a and 16a of the diaphragms 14 and 16, fixed on the valve body 8 and forming the power pistons in order to communicate the variable pressure chambers 5b and 7b divided by the diaphragms 14 and 16 with the passages 26 and 28 corresponding to the variable pressure chambers 5b and 7b. Accordingly, the air passages are opened to the variable pressure chambers 5b and 7b through the groove 27 formed on the beads 14a and 16a of the diaphragms 14 and 16. According to this invention, therefore, there is no need to provide wide gap between the fixed portion of the beads and the center plate in order to open the air passages to the variable pressure chambers. This makes it possible to shorten overall length of the negative pressure booster equipment 1.

What we claim is: 
     
       1. A negative pressure booster equipment, comprising a predetermined number of center plates, which divide the space formed by a front shell and a rear shell into two or more chambers, a valve body passing through said center plates and said rear shell airtightly and movably, power pistons coupled with the valve body and arranged in said two or more chambers and dividing these chambers into constant pressure chambers where negative pressure is introduced and variable pressure chambers where the air of atmospheric pressure is introduced during operation and said power pistons being provided as many as said chambers, a valve plunger mounted slidably on said valve body, an input shaft coupled with the valve plunger and disposed within said valve body movably back and forth, and a control vale, disposed in said valve body and operated by said valve plunger to selectively switch over the communication of each of said variable pressure chambers with the atmospheric air or with each of said constant pressure chambers through the passages formed by said valve body, characterized in that each of said power pistons is provided with a diaphragm having the inner peripheral beads fixed on said valve body, and that a groove is provided on the inner peripheral bead of at least one of said diaphragms in order to communicate said variable pressure chambers divided by said diaphragm with said passages corresponding to said variable pressure chambers. 
     
     
       2. A negative pressure booster according to claim 1, wherein said inner peripheral bead of said diaphragm is provided with two or more radial grooves, and at least one of the grooves communicates with said passage corresponding to said variable pressure chamber. 
     
     
       3. A negative pressure booster according to claim 2, wherein said groove as formed on said inner peripheral bead of said diaphragm consists of a first groove extending to radial direction and a second groove extending to axial direction, and said first and second grooves are communicated with each other.